Polyamide resins represented by nylon 6 and nylon 66 have excellent characteristics as engineering plastics and are widely used in various industrial fields such as automotive and electric and electronic fields.
In recent years, in automobile parts, especially resin-made parts to be used within an engine room, following high performance and high output of engines, the use environment becomes severe such that the temperature of engine cooling water increases and that the temperature within the engine room increases. Also, in the cold district, a large amount of a road-antifreezing agent is sprayed as a snow-melting agent, and engine parts are exposed to such chemicals. Now, a request for materials capable of keeping functions such as high strength and dimensional stability even in such a severe use environment is very raised.
However, in generalizably used nylon 6 and nylon 66, in particular, road-antifreezing agents made of a metal salt such as calcium chloride and zinc chloride act to the cycle of drying and wetting as repeated by water absorption by contact with engine cooling water and an increase in temperature within the engine room, resulting in a problem that stress cracking is liable to occur.
Then, as a method of improving the resistance to calcium chloride of nylon 6 and nylon 66, it is proposed to compound nylon 6 or nylon 66 with a polyamide resin having excellent resistance to calcium chloride such as nylon 12 (see, for example, JP-A-57-212252 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”.)). However, under the foregoing severe use environment, the resistance to calcium chloride is not sufficiently improved, and nylon 6 or nylon 66 does not substantially have an affinity with nylon 12, resulting in a problem that the weld line strength becomes worse.
Also, there is proposed a method of improving the resistance to calcium chloride by compounding nylon 6 or nylon 66 with a high-heat-resistant copolyamide resin containing an aromatic component such as a terephthalic acid unit and an isophthalic acid unit (see, for example, JP-A-58-53950 and JP-A-2002-114905). However, in order to improve the resistance to calcium chloride, though it is necessary to compound a large amount (30% by weight or more) of the foregoing high-heat-resistant copolyamide resin, since the foregoing high-heat-resistant copolyamide resin is amorphous, the viscosity becomes high, resulting in a problem that the fluidity becomes worse to deteriorate the appearance of molded articles.